1. Field of the Invention
The present invention relates to a disc apparatus, and more particular to a method for assembling a disc-like recording medium in a rotary shaft of a disc apparatus.
2. Description of Prior Art
A disc apparatus, for example, a magnetic disc apparatus is structured such that a magnetic head is floated in a fine gap due to a pneumatic pressure generated by a rotation of a disc so as to read and write a magnetic record.
In recent years, in order to improve a recording density accompanying with a reduction of size and an increase of capacity of the disc apparatus mentioned above, there have been developed a method of improving an accuracy for positioning an information recording/writing head on a track of a recorded information formed on the disc so as to increase a density of the recording track, and a method of reducing a gap between a head and a surface of a disc medium so as to reduce a bit length in a relative moving direction between the head and the disc and increase a density.
In these methods, if the clamped disc assembly does not have a good balance of rotation, a shaft deflection vibration is increased at a time of rotating the disc, whereby an accuracy in a positioning direction is deteriorated. Further, a vibration in a vertical direction due to an unbalance of rotation rounds into a fluctuation of flying height. Accordingly, it is necessary that the disc assembly satisfies the balance of rotation.
As a method for preventing the unbalance of rotation as mentioned above, there has been conventionally proposed various kinds of methods. For example, in Japanese Unexamined Patent Publication No. 10-149616, there is disclosed a magnetic disc apparatus employing a plurality of discs in an overlapping manner, in which the discs are biased at a tolerance between a motor hub and a fixing hole of the discs, whereby a center of gravity of all combined discs is coincided with a center of a spindle motor. In the structure, for example, in the case of two discs, the discs are biased in direct opposition at a tolerance, and in the case of three discs, the discs are biased at 120 degrees.
In the prior art mentioned above, the assembling step is easily executed, however, in accordance with this method, an inner diameter of the disc and a side surface of the hub are in contact with each other at any area on a circumference. In this state, in the case that the hub is deformed due to a heating and cooling operation or an impact application, a non-isotropic deformation is generated in the discs, whereby there is a risk that a deterioration of positioning accuracy rounds into generation.